The present invention generally relates to flight guidance and control systems for intercepting air or space crafts, and particularly to an advanced guidance system and method for homing missiles that provide improved performance in the terminal phase near target intercept.
Previous guidance systems were founded on basic and improved Proportional Navigation. In this regard, the U.S. Pat. Nos. 4,456,862, 4,492,352, 4,494,202, and 4,502,650 to William R. Yueh provide a good example of a terminal guidance system for missiles which employs improved proportional navigation techniques. Nevertheless, previous guidance systems have generally not given detailed attention to the stability of the control system in the last moments before intercept. More specifically, in most previous homing guidance laws, there is a built-in instability near intercept that causes a miss when disturbances occur (e.g., new information or new target maneuvers or terminal area sensor or target generated noise) after the system is nearing instability. As a result, these control systems have gone into the `end game` in a marginally stable or unstable condition. Any transient input to the control system can increase the probability of causing the beginning of a divergent oscillation, which in turn, could cause a miss at intercept.
Additionally, previous guidance and control systems have tended to design the `autopilot` and the `guidance` system independently, and have failed to consider all of the destabilizing influences of the autopilot saturation nonlinearities on the entire guidance and control system. Often, this has resulted in a more conservative design than was necessary, and as indicated above, a design in which the control system was unstable at intercept. As a result, there is a general rule of thumb that the control system must have about ten missile time constants to go at terminal sensor acquisition, and establishes the fact of system miss when the target maneuvers within ten, or so, time constants to go. It is also traditional that the missile acceleration capability should be three times the target acceleration capability.
Accordingly, it is a principal objective of the present invention to provide an advanced homing guidance system and method for directing a vehicle toward a target which substantially enhances performance near target intercept, such as the ability to respond to late target maneuvers.
It is another objective of the present invention to provide an advanced homing guidance system and method which embodies a unique conceptual coordinate system that relates the target body axes to the vehicle body axes.
It is a further objective of the present invention to provide an advanced homing guidance system and method which incorporates non-linear estimation techniques that segregate the relative velocity state from the relative position state, and to make maximum use of the physical attributes of the homing vehicle (e.g., its actuation power, control effectiveness, and lifting effectiveness).
It is an additional objective of the present invention to provide an advanced homing guidance system and method which enables a reduction in the required time constants to go at terminal sensor acquisition to two or three.
It is yet another objective of the present invention to provide an advanced homing guidance system and method which enables a reduction in the vehicle acceleration capability required from three to as little as two times the target acceleration capability.